src/expr.rs

   1 // Copyright 2015 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 use std::borrow::Cow;
  12 use std::cmp::min;
  13
  14 use config::lists::*;
  15 use syntax::parse::token::DelimToken;
  16 use syntax::source_map::{BytePos, SourceMap, Span};
  17 use syntax::{ast, ptr};
  18
  19 use chains::rewrite_chain;
  20 use closures;
  21 use comment::{
  22     combine_strs_with_missing_comments, contains_comment, recover_comment_removed, rewrite_comment,
  23     rewrite_missing_comment, CharClasses, FindUncommented,
  24 };
  25 use config::{Config, ControlBraceStyle, IndentStyle};
  26 use lists::{
  27     definitive_tactic, itemize_list, shape_for_tactic, struct_lit_formatting, struct_lit_shape,
  28     struct_lit_tactic, write_list, ListFormatting, ListItem, Separator,
  29 };
  30 use macros::{rewrite_macro, MacroPosition};
  31 use matches::rewrite_match;
  32 use overflow::{self, IntoOverflowableItem, OverflowableItem};
  33 use pairs::{rewrite_all_pairs, rewrite_pair, PairParts};
  34 use patterns::is_short_pattern;
  35 use rewrite::{Rewrite, RewriteContext};
  36 use shape::{Indent, Shape};
  37 use source_map::{LineRangeUtils, SpanUtils};
  38 use spanned::Spanned;
  39 use string::{rewrite_string, StringFormat};
  40 use types::{rewrite_path, PathContext};
  41 use utils::{
  42     colon_spaces, contains_skip, count_newlines, first_line_ends_with, inner_attributes,
  43     last_line_extendable, last_line_width, mk_sp, outer_attributes, ptr_vec_to_ref_vec,
  44     semicolon_for_stmt, wrap_str,
  45 };
  46 use vertical::rewrite_with_alignment;
  47 use visitor::FmtVisitor;
  48
  49 impl Rewrite for ast::Expr {
  50     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
  51         format_expr(self, ExprType::SubExpression, context, shape)
  52     }
  53 }
  54
  55 #[derive(Copy, Clone, PartialEq)]
  56 pub enum ExprType {
  57     Statement,
  58     SubExpression,
  59 }
  60
  61 pub fn format_expr(
  62     expr: &ast::Expr,
  63     expr_type: ExprType,
  64     context: &RewriteContext,
  65     shape: Shape,
  66 ) -> Option<String> {
  67     skip_out_of_file_lines_range!(context, expr.span);
  68
  69     if contains_skip(&*expr.attrs) {
  70         return Some(context.snippet(expr.span()).to_owned());
  71     }
  72
  73     let expr_rw = match expr.node {
  74         ast::ExprKind::Array(ref expr_vec) => rewrite_array(
  75             "",
  76             expr_vec.iter(),
  77             expr.span,
  78             context,
  79             shape,
  80             choose_separator_tactic(context, expr.span),
  81             None,
  82         ),
  83         ast::ExprKind::Lit(ref l) => rewrite_literal(context, l, shape),
  84         ast::ExprKind::Call(ref callee, ref args) => {
  85             let inner_span = mk_sp(callee.span.hi(), expr.span.hi());
  86             let callee_str = callee.rewrite(context, shape)?;
  87             rewrite_call(context, &callee_str, args, inner_span, shape)
  88         }
  89         ast::ExprKind::Paren(ref subexpr) => rewrite_paren(context, subexpr, shape, expr.span),
  90         ast::ExprKind::Binary(op, ref lhs, ref rhs) => {
  91             // FIXME: format comments between operands and operator
  92             rewrite_all_pairs(expr, shape, context).or_else(|| {
  93                 rewrite_pair(
  94                     &**lhs,
  95                     &**rhs,
  96                     PairParts::infix(&format!(" {} ", context.snippet(op.span))),
  97                     context,
  98                     shape,
  99                     context.config.binop_separator(),
 100                 )
 101             })
 102         }
 103         ast::ExprKind::Unary(op, ref subexpr) => rewrite_unary_op(context, op, subexpr, shape),
 104         ast::ExprKind::Struct(ref path, ref fields, ref base) => rewrite_struct_lit(
 105             context,
 106             path,
 107             fields,
 108             base.as_ref().map(|e| &**e),
 109             expr.span,
 110             shape,
 111         ),
 112         ast::ExprKind::Tup(ref items) => {
 113             rewrite_tuple(context, items.iter(), expr.span, shape, items.len() == 1)
 114         }
 115         ast::ExprKind::If(..)
 116         | ast::ExprKind::IfLet(..)
 117         | ast::ExprKind::ForLoop(..)
 118         | ast::ExprKind::Loop(..)
 119         | ast::ExprKind::While(..)
 120         | ast::ExprKind::WhileLet(..) => to_control_flow(expr, expr_type)
 121             .and_then(|control_flow| control_flow.rewrite(context, shape)),
 122         ast::ExprKind::Block(ref block, opt_label) => {
 123             match expr_type {
 124                 ExprType::Statement => {
 125                     if is_unsafe_block(block) {
 126                         rewrite_block(block, Some(&expr.attrs), opt_label, context, shape)
 127                     } else if let rw @ Some(_) =
 128                         rewrite_empty_block(context, block, Some(&expr.attrs), opt_label, "", shape)
 129                     {
 130                         // Rewrite block without trying to put it in a single line.
 131                         rw
 132                     } else {
 133                         let prefix = block_prefix(context, block, shape)?;
 134
 135                         rewrite_block_with_visitor(
 136                             context,
 137                             &prefix,
 138                             block,
 139                             Some(&expr.attrs),
 140                             opt_label,
 141                             shape,
 142                             true,
 143                         )
 144                     }
 145                 }
 146                 ExprType::SubExpression => {
 147                     rewrite_block(block, Some(&expr.attrs), opt_label, context, shape)
 148                 }
 149             }
 150         }
 151         ast::ExprKind::Match(ref cond, ref arms) => {
 152             rewrite_match(context, cond, arms, shape, expr.span, &expr.attrs)
 153         }
 154         ast::ExprKind::Path(ref qself, ref path) => {
 155             rewrite_path(context, PathContext::Expr, qself.as_ref(), path, shape)
 156         }
 157         ast::ExprKind::Assign(ref lhs, ref rhs) => {
 158             rewrite_assignment(context, lhs, rhs, None, shape)
 159         }
 160         ast::ExprKind::AssignOp(ref op, ref lhs, ref rhs) => {
 161             rewrite_assignment(context, lhs, rhs, Some(op), shape)
 162         }
 163         ast::ExprKind::Continue(ref opt_label) => {
 164             let id_str = match *opt_label {
 165                 Some(label) => format!(" {}", label.ident),
 166                 None => String::new(),
 167             };
 168             Some(format!("continue{}", id_str))
 169         }
 170         ast::ExprKind::Break(ref opt_label, ref opt_expr) => {
 171             let id_str = match *opt_label {
 172                 Some(label) => format!(" {}", label.ident),
 173                 None => String::new(),
 174             };
 175
 176             if let Some(ref expr) = *opt_expr {
 177                 rewrite_unary_prefix(context, &format!("break{} ", id_str), &**expr, shape)
 178             } else {
 179                 Some(format!("break{}", id_str))
 180             }
 181         }
 182         ast::ExprKind::Yield(ref opt_expr) => {
 183             if let Some(ref expr) = *opt_expr {
 184                 rewrite_unary_prefix(context, "yield ", &**expr, shape)
 185             } else {
 186                 Some("yield".to_string())
 187             }
 188         }
 189         ast::ExprKind::Closure(capture, asyncness, movability, ref fn_decl, ref body, _) => {
 190             closures::rewrite_closure(
 191                 capture, asyncness, movability, fn_decl, body, expr.span, context, shape,
 192             )
 193         }
 194         ast::ExprKind::Try(..) | ast::ExprKind::Field(..) | ast::ExprKind::MethodCall(..) => {
 195             rewrite_chain(expr, context, shape)
 196         }
 197         ast::ExprKind::Mac(ref mac) => {
 198             rewrite_macro(mac, None, context, shape, MacroPosition::Expression).or_else(|| {
 199                 wrap_str(
 200                     context.snippet(expr.span).to_owned(),
 201                     context.config.max_width(),
 202                     shape,
 203                 )
 204             })
 205         }
 206         ast::ExprKind::Ret(None) => Some("return".to_owned()),
 207         ast::ExprKind::Ret(Some(ref expr)) => {
 208             rewrite_unary_prefix(context, "return ", &**expr, shape)
 209         }
 210         ast::ExprKind::Box(ref expr) => rewrite_unary_prefix(context, "box ", &**expr, shape),
 211         ast::ExprKind::AddrOf(mutability, ref expr) => {
 212             rewrite_expr_addrof(context, mutability, expr, shape)
 213         }
 214         ast::ExprKind::Cast(ref expr, ref ty) => rewrite_pair(
 215             &**expr,
 216             &**ty,
 217             PairParts::infix(" as "),
 218             context,
 219             shape,
 220             SeparatorPlace::Front,
 221         ),
 222         ast::ExprKind::Type(ref expr, ref ty) => rewrite_pair(
 223             &**expr,
 224             &**ty,
 225             PairParts::infix(": "),
 226             context,
 227             shape,
 228             SeparatorPlace::Back,
 229         ),
 230         ast::ExprKind::Index(ref expr, ref index) => {
 231             rewrite_index(&**expr, &**index, context, shape)
 232         }
 233         ast::ExprKind::Repeat(ref expr, ref repeats) => rewrite_pair(
 234             &**expr,
 235             &*repeats.value,
 236             PairParts::new("[", "; ", "]"),
 237             context,
 238             shape,
 239             SeparatorPlace::Back,
 240         ),
 241         ast::ExprKind::Range(ref lhs, ref rhs, limits) => {
 242             let delim = match limits {
 243                 ast::RangeLimits::HalfOpen => "..",
 244                 ast::RangeLimits::Closed => "..=",
 245             };
 246
 247             fn needs_space_before_range(context: &RewriteContext, lhs: &ast::Expr) -> bool {
 248                 match lhs.node {
 249                     ast::ExprKind::Lit(ref lit) => match lit.node {
 250                         ast::LitKind::FloatUnsuffixed(..) => {
 251                             context.snippet(lit.span).ends_with('.')
 252                         }
 253                         _ => false,
 254                     },
 255                     _ => false,
 256                 }
 257             }
 258
 259             fn needs_space_after_range(rhs: &ast::Expr) -> bool {
 260                 match rhs.node {
 261                     // Don't format `.. ..` into `....`, which is invalid.
 262                     //
 263                     // This check is unnecessary for `lhs`, because a range
 264                     // starting from another range needs parentheses as `(x ..) ..`
 265                     // (`x .. ..` is a range from `x` to `..`).
 266                     ast::ExprKind::Range(None, _, _) => true,
 267                     _ => false,
 268                 }
 269             }
 270
 271             let default_sp_delim = |lhs: Option<&ast::Expr>, rhs: Option<&ast::Expr>| {
 272                 let space_if = |b: bool| if b { " " } else { "" };
 273
 274                 format!(
 275                     "{}{}{}",
 276                     lhs.map(|lhs| space_if(needs_space_before_range(context, lhs)))
 277                         .unwrap_or(""),
 278                     delim,
 279                     rhs.map(|rhs| space_if(needs_space_after_range(rhs)))
 280                         .unwrap_or(""),
 281                 )
 282             };
 283
 284             match (lhs.as_ref().map(|x| &**x), rhs.as_ref().map(|x| &**x)) {
 285                 (Some(lhs), Some(rhs)) => {
 286                     let sp_delim = if context.config.spaces_around_ranges() {
 287                         format!(" {} ", delim)
 288                     } else {
 289                         default_sp_delim(Some(lhs), Some(rhs))
 290                     };
 291                     rewrite_pair(
 292                         &*lhs,
 293                         &*rhs,
 294                         PairParts::infix(&sp_delim),
 295                         context,
 296                         shape,
 297                         context.config.binop_separator(),
 298                     )
 299                 }
 300                 (None, Some(rhs)) => {
 301                     let sp_delim = if context.config.spaces_around_ranges() {
 302                         format!("{} ", delim)
 303                     } else {
 304                         default_sp_delim(None, Some(rhs))
 305                     };
 306                     rewrite_unary_prefix(context, &sp_delim, &*rhs, shape)
 307                 }
 308                 (Some(lhs), None) => {
 309                     let sp_delim = if context.config.spaces_around_ranges() {
 310                         format!(" {}", delim)
 311                     } else {
 312                         default_sp_delim(Some(lhs), None)
 313                     };
 314                     rewrite_unary_suffix(context, &sp_delim, &*lhs, shape)
 315                 }
 316                 (None, None) => Some(delim.to_owned()),
 317             }
 318         }
 319         // We do not format these expressions yet, but they should still
 320         // satisfy our width restrictions.
 321         ast::ExprKind::InlineAsm(..) => Some(context.snippet(expr.span).to_owned()),
 322         ast::ExprKind::TryBlock(ref block) => {
 323             if let rw @ Some(_) =
 324                 rewrite_single_line_block(context, "try ", block, Some(&expr.attrs), None, shape)
 325             {
 326                 rw
 327             } else {
 328                 // 9 = `try `
 329                 let budget = shape.width.saturating_sub(9);
 330                 Some(format!(
 331                     "{}{}",
 332                     "try ",
 333                     rewrite_block(
 334                         block,
 335                         Some(&expr.attrs),
 336                         None,
 337                         context,
 338                         Shape::legacy(budget, shape.indent)
 339                     )?
 340                 ))
 341             }
 342         }
 343         ast::ExprKind::ObsoleteInPlace(ref lhs, ref rhs) => lhs
 344             .rewrite(context, shape)
 345             .map(|s| s + " <-")
 346             .and_then(|lhs| rewrite_assign_rhs(context, lhs, &**rhs, shape)),
 347         ast::ExprKind::Async(capture_by, _node_id, ref block) => {
 348             let mover = if capture_by == ast::CaptureBy::Value {
 349                 "move "
 350             } else {
 351                 ""
 352             };
 353             if let rw @ Some(_) = rewrite_single_line_block(
 354                 context,
 355                 format!("{}{}", "async ", mover).as_str(),
 356                 block,
 357                 Some(&expr.attrs),
 358                 None,
 359                 shape,
 360             ) {
 361                 rw
 362             } else {
 363                 // 6 = `async `
 364                 let budget = shape.width.saturating_sub(6);
 365                 Some(format!(
 366                     "{}{}{}",
 367                     "async ",
 368                     mover,
 369                     rewrite_block(
 370                         block,
 371                         Some(&expr.attrs),
 372                         None,
 373                         context,
 374                         Shape::legacy(budget, shape.indent)
 375                     )?
 376                 ))
 377             }
 378         }
 379     };
 380
 381     expr_rw
 382         .and_then(|expr_str| recover_comment_removed(expr_str, expr.span, context))
 383         .and_then(|expr_str| {
 384             let attrs = outer_attributes(&expr.attrs);
 385             let attrs_str = attrs.rewrite(context, shape)?;
 386             let span = mk_sp(
 387                 attrs.last().map_or(expr.span.lo(), |attr| attr.span.hi()),
 388                 expr.span.lo(),
 389             );
 390             combine_strs_with_missing_comments(context, &attrs_str, &expr_str, span, shape, false)
 391         })
 392 }
 393
 394 pub fn rewrite_array<'a, T: 'a + IntoOverflowableItem<'a>>(
 395     name: &'a str,
 396     exprs: impl Iterator<Item = &'a T>,
 397     span: Span,
 398     context: &'a RewriteContext,
 399     shape: Shape,
 400     force_separator_tactic: Option<SeparatorTactic>,
 401     delim_token: Option<DelimToken>,
 402 ) -> Option<String> {
 403     overflow::rewrite_with_square_brackets(
 404         context,
 405         name,
 406         exprs,
 407         shape,
 408         span,
 409         force_separator_tactic,
 410         delim_token,
 411     )
 412 }
 413
 414 fn rewrite_empty_block(
 415     context: &RewriteContext,
 416     block: &ast::Block,
 417     attrs: Option<&[ast::Attribute]>,
 418     label: Option<ast::Label>,
 419     prefix: &str,
 420     shape: Shape,
 421 ) -> Option<String> {
 422     let label_str = rewrite_label(label);
 423     if attrs.map_or(false, |a| !inner_attributes(a).is_empty()) {
 424         return None;
 425     }
 426
 427     if block.stmts.is_empty()
 428         && !block_contains_comment(block, context.source_map)
 429         && shape.width >= 2
 430     {
 431         return Some(format!("{}{}{{}}", prefix, label_str));
 432     }
 433
 434     // If a block contains only a single-line comment, then leave it on one line.
 435     let user_str = context.snippet(block.span);
 436     let user_str = user_str.trim();
 437     if user_str.starts_with('{') && user_str.ends_with('}') {
 438         let comment_str = user_str[1..user_str.len() - 1].trim();
 439         if block.stmts.is_empty()
 440             && !comment_str.contains('\n')
 441             && !comment_str.starts_with("//")
 442             && comment_str.len() + 4 <= shape.width
 443         {
 444             return Some(format!("{}{}{{ {} }}", prefix, label_str, comment_str));
 445         }
 446     }
 447
 448     None
 449 }
 450
 451 fn block_prefix(context: &RewriteContext, block: &ast::Block, shape: Shape) -> Option<String> {
 452     Some(match block.rules {
 453         ast::BlockCheckMode::Unsafe(..) => {
 454             let snippet = context.snippet(block.span);
 455             let open_pos = snippet.find_uncommented("{")?;
 456             // Extract comment between unsafe and block start.
 457             let trimmed = &snippet[6..open_pos].trim();
 458
 459             if !trimmed.is_empty() {
 460                 // 9 = "unsafe  {".len(), 7 = "unsafe ".len()
 461                 let budget = shape.width.checked_sub(9)?;
 462                 format!(
 463                     "unsafe {} ",
 464                     rewrite_comment(
 465                         trimmed,
 466                         true,
 467                         Shape::legacy(budget, shape.indent + 7),
 468                         context.config,
 469                     )?
 470                 )
 471             } else {
 472                 "unsafe ".to_owned()
 473             }
 474         }
 475         ast::BlockCheckMode::Default => String::new(),
 476     })
 477 }
 478
 479 fn rewrite_single_line_block(
 480     context: &RewriteContext,
 481     prefix: &str,
 482     block: &ast::Block,
 483     attrs: Option<&[ast::Attribute]>,
 484     label: Option<ast::Label>,
 485     shape: Shape,
 486 ) -> Option<String> {
 487     if is_simple_block(block, attrs, context.source_map) {
 488         let expr_shape = shape.offset_left(last_line_width(prefix))?;
 489         let expr_str = block.stmts[0].rewrite(context, expr_shape)?;
 490         let label_str = rewrite_label(label);
 491         let result = format!("{}{}{{ {} }}", prefix, label_str, expr_str);
 492         if result.len() <= shape.width && !result.contains('\n') {
 493             return Some(result);
 494         }
 495     }
 496     None
 497 }
 498
 499 pub fn rewrite_block_with_visitor(
 500     context: &RewriteContext,
 501     prefix: &str,
 502     block: &ast::Block,
 503     attrs: Option<&[ast::Attribute]>,
 504     label: Option<ast::Label>,
 505     shape: Shape,
 506     has_braces: bool,
 507 ) -> Option<String> {
 508     if let rw @ Some(_) = rewrite_empty_block(context, block, attrs, label, prefix, shape) {
 509         return rw;
 510     }
 511
 512     let mut visitor = FmtVisitor::from_context(context);
 513     visitor.block_indent = shape.indent;
 514     visitor.is_if_else_block = context.is_if_else_block();
 515     match block.rules {
 516         ast::BlockCheckMode::Unsafe(..) => {
 517             let snippet = context.snippet(block.span);
 518             let open_pos = snippet.find_uncommented("{")?;
 519             visitor.last_pos = block.span.lo() + BytePos(open_pos as u32)
 520         }
 521         ast::BlockCheckMode::Default => visitor.last_pos = block.span.lo(),
 522     }
 523
 524     let inner_attrs = attrs.map(inner_attributes);
 525     let label_str = rewrite_label(label);
 526     visitor.visit_block(block, inner_attrs.as_ref().map(|a| &**a), has_braces);
 527     Some(format!("{}{}{}", prefix, label_str, visitor.buffer))
 528 }
 529
 530 impl Rewrite for ast::Block {
 531     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 532         rewrite_block(self, None, None, context, shape)
 533     }
 534 }
 535
 536 fn rewrite_block(
 537     block: &ast::Block,
 538     attrs: Option<&[ast::Attribute]>,
 539     label: Option<ast::Label>,
 540     context: &RewriteContext,
 541     shape: Shape,
 542 ) -> Option<String> {
 543     let prefix = block_prefix(context, block, shape)?;
 544
 545     // shape.width is used only for the single line case: either the empty block `{}`,
 546     // or an unsafe expression `unsafe { e }`.
 547     if let rw @ Some(_) = rewrite_empty_block(context, block, attrs, label, &prefix, shape) {
 548         return rw;
 549     }
 550
 551     let result = rewrite_block_with_visitor(context, &prefix, block, attrs, label, shape, true);
 552     if let Some(ref result_str) = result {
 553         if result_str.lines().count() <= 3 {
 554             if let rw @ Some(_) =
 555                 rewrite_single_line_block(context, &prefix, block, attrs, label, shape)
 556             {
 557                 return rw;
 558             }
 559         }
 560     }
 561
 562     result
 563 }
 564
 565 impl Rewrite for ast::Stmt {
 566     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 567         skip_out_of_file_lines_range!(context, self.span());
 568
 569         let result = match self.node {
 570             ast::StmtKind::Local(ref local) => local.rewrite(context, shape),
 571             ast::StmtKind::Expr(ref ex) | ast::StmtKind::Semi(ref ex) => {
 572                 let suffix = if semicolon_for_stmt(context, self) {
 573                     ";"
 574                 } else {
 575                     ""
 576                 };
 577
 578                 let shape = shape.sub_width(suffix.len())?;
 579                 format_expr(ex, ExprType::Statement, context, shape).map(|s| s + suffix)
 580             }
 581             ast::StmtKind::Mac(..) | ast::StmtKind::Item(..) => None,
 582         };
 583         result.and_then(|res| recover_comment_removed(res, self.span(), context))
 584     }
 585 }
 586
 587 // Rewrite condition if the given expression has one.
 588 pub fn rewrite_cond(context: &RewriteContext, expr: &ast::Expr, shape: Shape) -> Option<String> {
 589     match expr.node {
 590         ast::ExprKind::Match(ref cond, _) => {
 591             // `match `cond` {`
 592             let cond_shape = match context.config.indent_style() {
 593                 IndentStyle::Visual => shape.shrink_left(6).and_then(|s| s.sub_width(2))?,
 594                 IndentStyle::Block => shape.offset_left(8)?,
 595             };
 596             cond.rewrite(context, cond_shape)
 597         }
 598         _ => to_control_flow(expr, ExprType::SubExpression).and_then(|control_flow| {
 599             let alt_block_sep =
 600                 String::from("\n") + &shape.indent.block_only().to_string(context.config);
 601             control_flow
 602                 .rewrite_cond(context, shape, &alt_block_sep)
 603                 .and_then(|rw| Some(rw.0))
 604         }),
 605     }
 606 }
 607
 608 // Abstraction over control flow expressions
 609 #[derive(Debug)]
 610 struct ControlFlow<'a> {
 611     cond: Option<&'a ast::Expr>,
 612     block: &'a ast::Block,
 613     else_block: Option<&'a ast::Expr>,
 614     label: Option<ast::Label>,
 615     pats: Vec<&'a ast::Pat>,
 616     keyword: &'a str,
 617     matcher: &'a str,
 618     connector: &'a str,
 619     allow_single_line: bool,
 620     // True if this is an `if` expression in an `else if` :-( hacky
 621     nested_if: bool,
 622     span: Span,
 623 }
 624
 625 fn to_control_flow(expr: &ast::Expr, expr_type: ExprType) -> Option<ControlFlow> {
 626     match expr.node {
 627         ast::ExprKind::If(ref cond, ref if_block, ref else_block) => Some(ControlFlow::new_if(
 628             cond,
 629             vec![],
 630             if_block,
 631             else_block.as_ref().map(|e| &**e),
 632             expr_type == ExprType::SubExpression,
 633             false,
 634             expr.span,
 635         )),
 636         ast::ExprKind::IfLet(ref pat, ref cond, ref if_block, ref else_block) => {
 637             Some(ControlFlow::new_if(
 638                 cond,
 639                 ptr_vec_to_ref_vec(pat),
 640                 if_block,
 641                 else_block.as_ref().map(|e| &**e),
 642                 expr_type == ExprType::SubExpression,
 643                 false,
 644                 expr.span,
 645             ))
 646         }
 647         ast::ExprKind::ForLoop(ref pat, ref cond, ref block, label) => {
 648             Some(ControlFlow::new_for(pat, cond, block, label, expr.span))
 649         }
 650         ast::ExprKind::Loop(ref block, label) => {
 651             Some(ControlFlow::new_loop(block, label, expr.span))
 652         }
 653         ast::ExprKind::While(ref cond, ref block, label) => Some(ControlFlow::new_while(
 654             vec![],
 655             cond,
 656             block,
 657             label,
 658             expr.span,
 659         )),
 660         ast::ExprKind::WhileLet(ref pat, ref cond, ref block, label) => Some(
 661             ControlFlow::new_while(ptr_vec_to_ref_vec(pat), cond, block, label, expr.span),
 662         ),
 663         _ => None,
 664     }
 665 }
 666
 667 fn choose_matcher(pats: &[&ast::Pat]) -> &'static str {
 668     if pats.is_empty() {
 669         ""
 670     } else {
 671         "let"
 672     }
 673 }
 674
 675 impl<'a> ControlFlow<'a> {
 676     fn new_if(
 677         cond: &'a ast::Expr,
 678         pats: Vec<&'a ast::Pat>,
 679         block: &'a ast::Block,
 680         else_block: Option<&'a ast::Expr>,
 681         allow_single_line: bool,
 682         nested_if: bool,
 683         span: Span,
 684     ) -> ControlFlow<'a> {
 685         let matcher = choose_matcher(&pats);
 686         ControlFlow {
 687             cond: Some(cond),
 688             block,
 689             else_block,
 690             label: None,
 691             pats,
 692             keyword: "if",
 693             matcher,
 694             connector: " =",
 695             allow_single_line,
 696             nested_if,
 697             span,
 698         }
 699     }
 700
 701     fn new_loop(block: &'a ast::Block, label: Option<ast::Label>, span: Span) -> ControlFlow<'a> {
 702         ControlFlow {
 703             cond: None,
 704             block,
 705             else_block: None,
 706             label,
 707             pats: vec![],
 708             keyword: "loop",
 709             matcher: "",
 710             connector: "",
 711             allow_single_line: false,
 712             nested_if: false,
 713             span,
 714         }
 715     }
 716
 717     fn new_while(
 718         pats: Vec<&'a ast::Pat>,
 719         cond: &'a ast::Expr,
 720         block: &'a ast::Block,
 721         label: Option<ast::Label>,
 722         span: Span,
 723     ) -> ControlFlow<'a> {
 724         let matcher = choose_matcher(&pats);
 725         ControlFlow {
 726             cond: Some(cond),
 727             block,
 728             else_block: None,
 729             label,
 730             pats,
 731             keyword: "while",
 732             matcher,
 733             connector: " =",
 734             allow_single_line: false,
 735             nested_if: false,
 736             span,
 737         }
 738     }
 739
 740     fn new_for(
 741         pat: &'a ast::Pat,
 742         cond: &'a ast::Expr,
 743         block: &'a ast::Block,
 744         label: Option<ast::Label>,
 745         span: Span,
 746     ) -> ControlFlow<'a> {
 747         ControlFlow {
 748             cond: Some(cond),
 749             block,
 750             else_block: None,
 751             label,
 752             pats: vec![pat],
 753             keyword: "for",
 754             matcher: "",
 755             connector: " in",
 756             allow_single_line: false,
 757             nested_if: false,
 758             span,
 759         }
 760     }
 761
 762     fn rewrite_single_line(
 763         &self,
 764         pat_expr_str: &str,
 765         context: &RewriteContext,
 766         width: usize,
 767     ) -> Option<String> {
 768         assert!(self.allow_single_line);
 769         let else_block = self.else_block?;
 770         let fixed_cost = self.keyword.len() + "  {  } else {  }".len();
 771
 772         if let ast::ExprKind::Block(ref else_node, _) = else_block.node {
 773             if !is_simple_block(self.block, None, context.source_map)
 774                 || !is_simple_block(else_node, None, context.source_map)
 775                 || pat_expr_str.contains('\n')
 776             {
 777                 return None;
 778             }
 779
 780             let new_width = width.checked_sub(pat_expr_str.len() + fixed_cost)?;
 781             let expr = &self.block.stmts[0];
 782             let if_str = expr.rewrite(context, Shape::legacy(new_width, Indent::empty()))?;
 783
 784             let new_width = new_width.checked_sub(if_str.len())?;
 785             let else_expr = &else_node.stmts[0];
 786             let else_str = else_expr.rewrite(context, Shape::legacy(new_width, Indent::empty()))?;
 787
 788             if if_str.contains('\n') || else_str.contains('\n') {
 789                 return None;
 790             }
 791
 792             let result = format!(
 793                 "{} {} {{ {} }} else {{ {} }}",
 794                 self.keyword, pat_expr_str, if_str, else_str
 795             );
 796
 797             if result.len() <= width {
 798                 return Some(result);
 799             }
 800         }
 801
 802         None
 803     }
 804 }
 805
 806 impl<'a> ControlFlow<'a> {
 807     fn rewrite_pat_expr(
 808         &self,
 809         context: &RewriteContext,
 810         expr: &ast::Expr,
 811         shape: Shape,
 812         offset: usize,
 813     ) -> Option<String> {
 814         debug!("rewrite_pat_expr {:?} {:?} {:?}", shape, self.pats, expr);
 815
 816         let cond_shape = shape.offset_left(offset)?;
 817         if !self.pats.is_empty() {
 818             let matcher = if self.matcher.is_empty() {
 819                 self.matcher.to_owned()
 820             } else {
 821                 format!("{} ", self.matcher)
 822             };
 823             let pat_shape = cond_shape
 824                 .offset_left(matcher.len())?
 825                 .sub_width(self.connector.len())?;
 826             let pat_string = rewrite_multiple_patterns(context, &self.pats, pat_shape)?;
 827             let result = format!("{}{}{}", matcher, pat_string, self.connector);
 828             return rewrite_assign_rhs(context, result, expr, cond_shape);
 829         }
 830
 831         let expr_rw = expr.rewrite(context, cond_shape);
 832         // The expression may (partially) fit on the current line.
 833         // We do not allow splitting between `if` and condition.
 834         if self.keyword == "if" || expr_rw.is_some() {
 835             return expr_rw;
 836         }
 837
 838         // The expression won't fit on the current line, jump to next.
 839         let nested_shape = shape
 840             .block_indent(context.config.tab_spaces())
 841             .with_max_width(context.config);
 842         let nested_indent_str = nested_shape.indent.to_string_with_newline(context.config);
 843         expr.rewrite(context, nested_shape)
 844             .map(|expr_rw| format!("{}{}", nested_indent_str, expr_rw))
 845     }
 846
 847     fn rewrite_cond(
 848         &self,
 849         context: &RewriteContext,
 850         shape: Shape,
 851         alt_block_sep: &str,
 852     ) -> Option<(String, usize)> {
 853         // Do not take the rhs overhead from the upper expressions into account
 854         // when rewriting pattern.
 855         let new_width = context.budget(shape.used_width());
 856         let fresh_shape = Shape {
 857             width: new_width,
 858             ..shape
 859         };
 860         let constr_shape = if self.nested_if {
 861             // We are part of an if-elseif-else chain. Our constraints are tightened.
 862             // 7 = "} else " .len()
 863             fresh_shape.offset_left(7)?
 864         } else {
 865             fresh_shape
 866         };
 867
 868         let label_string = rewrite_label(self.label);
 869         // 1 = space after keyword.
 870         let offset = self.keyword.len() + label_string.len() + 1;
 871
 872         let pat_expr_string = match self.cond {
 873             Some(cond) => self.rewrite_pat_expr(context, cond, constr_shape, offset)?,
 874             None => String::new(),
 875         };
 876
 877         let brace_overhead =
 878             if context.config.control_brace_style() != ControlBraceStyle::AlwaysNextLine {
 879                 // 2 = ` {`
 880                 2
 881             } else {
 882                 0
 883             };
 884         let one_line_budget = context
 885             .config
 886             .max_width()
 887             .saturating_sub(constr_shape.used_width() + offset + brace_overhead);
 888         let force_newline_brace = (pat_expr_string.contains('\n')
 889             || pat_expr_string.len() > one_line_budget)
 890             && !last_line_extendable(&pat_expr_string);
 891
 892         // Try to format if-else on single line.
 893         if self.allow_single_line
 894             && context
 895                 .config
 896                 .width_heuristics()
 897                 .single_line_if_else_max_width
 898                 > 0
 899         {
 900             let trial = self.rewrite_single_line(&pat_expr_string, context, shape.width);
 901
 902             if let Some(cond_str) = trial {
 903                 if cond_str.len() <= context
 904                     .config
 905                     .width_heuristics()
 906                     .single_line_if_else_max_width
 907                 {
 908                     return Some((cond_str, 0));
 909                 }
 910             }
 911         }
 912
 913         let cond_span = if let Some(cond) = self.cond {
 914             cond.span
 915         } else {
 916             mk_sp(self.block.span.lo(), self.block.span.lo())
 917         };
 918
 919         // `for event in event`
 920         // Do not include label in the span.
 921         let lo = self
 922             .label
 923             .map_or(self.span.lo(), |label| label.ident.span.hi());
 924         let between_kwd_cond = mk_sp(
 925             context
 926                 .snippet_provider
 927                 .span_after(mk_sp(lo, self.span.hi()), self.keyword.trim()),
 928             if self.pats.is_empty() {
 929                 cond_span.lo()
 930             } else if self.matcher.is_empty() {
 931                 self.pats[0].span.lo()
 932             } else {
 933                 context
 934                     .snippet_provider
 935                     .span_before(self.span, self.matcher.trim())
 936             },
 937         );
 938
 939         let between_kwd_cond_comment = extract_comment(between_kwd_cond, context, shape);
 940
 941         let after_cond_comment =
 942             extract_comment(mk_sp(cond_span.hi(), self.block.span.lo()), context, shape);
 943
 944         let block_sep = if self.cond.is_none() && between_kwd_cond_comment.is_some() {
 945             ""
 946         } else if context.config.control_brace_style() == ControlBraceStyle::AlwaysNextLine
 947             || force_newline_brace
 948         {
 949             alt_block_sep
 950         } else {
 951             " "
 952         };
 953
 954         let used_width = if pat_expr_string.contains('\n') {
 955             last_line_width(&pat_expr_string)
 956         } else {
 957             // 2 = spaces after keyword and condition.
 958             label_string.len() + self.keyword.len() + pat_expr_string.len() + 2
 959         };
 960
 961         Some((
 962             format!(
 963                 "{}{}{}{}{}",
 964                 label_string,
 965                 self.keyword,
 966                 between_kwd_cond_comment.as_ref().map_or(
 967                     if pat_expr_string.is_empty() || pat_expr_string.starts_with('\n') {
 968                         ""
 969                     } else {
 970                         " "
 971                     },
 972                     |s| &**s,
 973                 ),
 974                 pat_expr_string,
 975                 after_cond_comment.as_ref().map_or(block_sep, |s| &**s)
 976             ),
 977             used_width,
 978         ))
 979     }
 980 }
 981
 982 impl<'a> Rewrite for ControlFlow<'a> {
 983     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 984         debug!("ControlFlow::rewrite {:?} {:?}", self, shape);
 985
 986         let alt_block_sep = &shape.indent.to_string_with_newline(context.config);
 987         let (cond_str, used_width) = self.rewrite_cond(context, shape, alt_block_sep)?;
 988         // If `used_width` is 0, it indicates that whole control flow is written in a single line.
 989         if used_width == 0 {
 990             return Some(cond_str);
 991         }
 992
 993         let block_width = shape.width.saturating_sub(used_width);
 994         // This is used only for the empty block case: `{}`. So, we use 1 if we know
 995         // we should avoid the single line case.
 996         let block_width = if self.else_block.is_some() || self.nested_if {
 997             min(1, block_width)
 998         } else {
 999             block_width
1000         };
1001         let block_shape = Shape {
1002             width: block_width,
1003             ..shape
1004         };
1005         let block_str = {
1006             let old_val = context.is_if_else_block.replace(self.else_block.is_some());
1007             let result =
1008                 rewrite_block_with_visitor(context, "", self.block, None, None, block_shape, true);
1009             context.is_if_else_block.replace(old_val);
1010             result?
1011         };
1012
1013         let mut result = format!("{}{}", cond_str, block_str);
1014
1015         if let Some(else_block) = self.else_block {
1016             let shape = Shape::indented(shape.indent, context.config);
1017             let mut last_in_chain = false;
1018             let rewrite = match else_block.node {
1019                 // If the else expression is another if-else expression, prevent it
1020                 // from being formatted on a single line.
1021                 // Note how we're passing the original shape, as the
1022                 // cost of "else" should not cascade.
1023                 ast::ExprKind::IfLet(ref pat, ref cond, ref if_block, ref next_else_block) => {
1024                     ControlFlow::new_if(
1025                         cond,
1026                         ptr_vec_to_ref_vec(pat),
1027                         if_block,
1028                         next_else_block.as_ref().map(|e| &**e),
1029                         false,
1030                         true,
1031                         mk_sp(else_block.span.lo(), self.span.hi()),
1032                     )
1033                     .rewrite(context, shape)
1034                 }
1035                 ast::ExprKind::If(ref cond, ref if_block, ref next_else_block) => {
1036                     ControlFlow::new_if(
1037                         cond,
1038                         vec![],
1039                         if_block,
1040                         next_else_block.as_ref().map(|e| &**e),
1041                         false,
1042                         true,
1043                         mk_sp(else_block.span.lo(), self.span.hi()),
1044                     )
1045                     .rewrite(context, shape)
1046                 }
1047                 _ => {
1048                     last_in_chain = true;
1049                     // When rewriting a block, the width is only used for single line
1050                     // blocks, passing 1 lets us avoid that.
1051                     let else_shape = Shape {
1052                         width: min(1, shape.width),
1053                         ..shape
1054                     };
1055                     format_expr(else_block, ExprType::Statement, context, else_shape)
1056                 }
1057             };
1058
1059             let between_kwd_else_block = mk_sp(
1060                 self.block.span.hi(),
1061                 context
1062                     .snippet_provider
1063                     .span_before(mk_sp(self.block.span.hi(), else_block.span.lo()), "else"),
1064             );
1065             let between_kwd_else_block_comment =
1066                 extract_comment(between_kwd_else_block, context, shape);
1067
1068             let after_else = mk_sp(
1069                 context
1070                     .snippet_provider
1071                     .span_after(mk_sp(self.block.span.hi(), else_block.span.lo()), "else"),
1072                 else_block.span.lo(),
1073             );
1074             let after_else_comment = extract_comment(after_else, context, shape);
1075
1076             let between_sep = match context.config.control_brace_style() {
1077                 ControlBraceStyle::AlwaysNextLine | ControlBraceStyle::ClosingNextLine => {
1078                     &*alt_block_sep
1079                 }
1080                 ControlBraceStyle::AlwaysSameLine => " ",
1081             };
1082             let after_sep = match context.config.control_brace_style() {
1083                 ControlBraceStyle::AlwaysNextLine if last_in_chain => &*alt_block_sep,
1084                 _ => " ",
1085             };
1086
1087             result.push_str(&format!(
1088                 "{}else{}",
1089                 between_kwd_else_block_comment
1090                     .as_ref()
1091                     .map_or(between_sep, |s| &**s),
1092                 after_else_comment.as_ref().map_or(after_sep, |s| &**s),
1093             ));
1094             result.push_str(&rewrite?);
1095         }
1096
1097         Some(result)
1098     }
1099 }
1100
1101 fn rewrite_label(opt_label: Option<ast::Label>) -> Cow<'static, str> {
1102     match opt_label {
1103         Some(label) => Cow::from(format!("{}: ", label.ident)),
1104         None => Cow::from(""),
1105     }
1106 }
1107
1108 fn extract_comment(span: Span, context: &RewriteContext, shape: Shape) -> Option<String> {
1109     match rewrite_missing_comment(span, shape, context) {
1110         Some(ref comment) if !comment.is_empty() => Some(format!(
1111             "{indent}{}{indent}",
1112             comment,
1113             indent = shape.indent.to_string_with_newline(context.config)
1114         )),
1115         _ => None,
1116     }
1117 }
1118
1119 pub fn block_contains_comment(block: &ast::Block, source_map: &SourceMap) -> bool {
1120     let snippet = source_map.span_to_snippet(block.span).unwrap();
1121     contains_comment(&snippet)
1122 }
1123
1124 // Checks that a block contains no statements, an expression and no comments or
1125 // attributes.
1126 // FIXME: incorrectly returns false when comment is contained completely within
1127 // the expression.
1128 pub fn is_simple_block(
1129     block: &ast::Block,
1130     attrs: Option<&[ast::Attribute]>,
1131     source_map: &SourceMap,
1132 ) -> bool {
1133     (block.stmts.len() == 1
1134         && stmt_is_expr(&block.stmts[0])
1135         && !block_contains_comment(block, source_map)
1136         && attrs.map_or(true, |a| a.is_empty()))
1137 }
1138
1139 /// Checks whether a block contains at most one statement or expression, and no
1140 /// comments or attributes.
1141 pub fn is_simple_block_stmt(
1142     block: &ast::Block,
1143     attrs: Option<&[ast::Attribute]>,
1144     source_map: &SourceMap,
1145 ) -> bool {
1146     block.stmts.len() <= 1
1147         && !block_contains_comment(block, source_map)
1148         && attrs.map_or(true, |a| a.is_empty())
1149 }
1150
1151 /// Checks whether a block contains no statements, expressions, comments, or
1152 /// inner attributes.
1153 pub fn is_empty_block(
1154     block: &ast::Block,
1155     attrs: Option<&[ast::Attribute]>,
1156     source_map: &SourceMap,
1157 ) -> bool {
1158     block.stmts.is_empty()
1159         && !block_contains_comment(block, source_map)
1160         && attrs.map_or(true, |a| inner_attributes(a).is_empty())
1161 }
1162
1163 pub fn stmt_is_expr(stmt: &ast::Stmt) -> bool {
1164     match stmt.node {
1165         ast::StmtKind::Expr(..) => true,
1166         _ => false,
1167     }
1168 }
1169
1170 pub fn is_unsafe_block(block: &ast::Block) -> bool {
1171     if let ast::BlockCheckMode::Unsafe(..) = block.rules {
1172         true
1173     } else {
1174         false
1175     }
1176 }
1177
1178 pub fn rewrite_multiple_patterns(
1179     context: &RewriteContext,
1180     pats: &[&ast::Pat],
1181     shape: Shape,
1182 ) -> Option<String> {
1183     let pat_strs = pats
1184         .iter()
1185         .map(|p| p.rewrite(context, shape))
1186         .collect::<Option<Vec<_>>>()?;
1187
1188     let use_mixed_layout = pats
1189         .iter()
1190         .zip(pat_strs.iter())
1191         .all(|(pat, pat_str)| is_short_pattern(pat, pat_str));
1192     let items: Vec<_> = pat_strs.into_iter().map(ListItem::from_str).collect();
1193     let tactic = if use_mixed_layout {
1194         DefinitiveListTactic::Mixed
1195     } else {
1196         definitive_tactic(
1197             &items,
1198             ListTactic::HorizontalVertical,
1199             Separator::VerticalBar,
1200             shape.width,
1201         )
1202     };
1203     let fmt = ListFormatting::new(shape, context.config)
1204         .tactic(tactic)
1205         .separator(" |")
1206         .separator_place(context.config.binop_separator())
1207         .ends_with_newline(false);
1208     write_list(&items, &fmt)
1209 }
1210
1211 pub fn rewrite_literal(context: &RewriteContext, l: &ast::Lit, shape: Shape) -> Option<String> {
1212     match l.node {
1213         ast::LitKind::Str(_, ast::StrStyle::Cooked) => rewrite_string_lit(context, l.span, shape),
1214         _ => wrap_str(
1215             context.snippet(l.span).to_owned(),
1216             context.config.max_width(),
1217             shape,
1218         ),
1219     }
1220 }
1221
1222 fn rewrite_string_lit(context: &RewriteContext, span: Span, shape: Shape) -> Option<String> {
1223     let string_lit = context.snippet(span);
1224
1225     if !context.config.format_strings() {
1226         if string_lit
1227             .lines()
1228             .rev()
1229             .skip(1)
1230             .all(|line| line.ends_with('\\'))
1231         {
1232             let new_indent = shape.visual_indent(1).indent;
1233             let indented_string_lit = String::from(
1234                 string_lit
1235                     .lines()
1236                     .map(|line| {
1237                         format!(
1238                             "{}{}",
1239                             new_indent.to_string(context.config),
1240                             line.trim_left()
1241                         )
1242                     })
1243                     .collect::<Vec<_>>()
1244                     .join("\n")
1245                     .trim_left(),
1246             );
1247             return wrap_str(indented_string_lit, context.config.max_width(), shape);
1248         } else {
1249             return wrap_str(string_lit.to_owned(), context.config.max_width(), shape);
1250         }
1251     }
1252
1253     // Remove the quote characters.
1254     let str_lit = &string_lit[1..string_lit.len() - 1];
1255
1256     rewrite_string(
1257         str_lit,
1258         &StringFormat::new(shape.visual_indent(0), context.config),
1259     )
1260 }
1261
1262 fn choose_separator_tactic(context: &RewriteContext, span: Span) -> Option<SeparatorTactic> {
1263     if context.inside_macro() {
1264         if span_ends_with_comma(context, span) {
1265             Some(SeparatorTactic::Always)
1266         } else {
1267             Some(SeparatorTactic::Never)
1268         }
1269     } else {
1270         None
1271     }
1272 }
1273
1274 pub fn rewrite_call(
1275     context: &RewriteContext,
1276     callee: &str,
1277     args: &[ptr::P<ast::Expr>],
1278     span: Span,
1279     shape: Shape,
1280 ) -> Option<String> {
1281     overflow::rewrite_with_parens(
1282         context,
1283         callee,
1284         args.iter(),
1285         shape,
1286         span,
1287         context.config.width_heuristics().fn_call_width,
1288         choose_separator_tactic(context, span),
1289     )
1290 }
1291
1292 pub fn is_simple_expr(expr: &ast::Expr) -> bool {
1293     match expr.node {
1294         ast::ExprKind::Lit(..) => true,
1295         ast::ExprKind::Path(ref qself, ref path) => qself.is_none() && path.segments.len() <= 1,
1296         ast::ExprKind::AddrOf(_, ref expr)
1297         | ast::ExprKind::Box(ref expr)
1298         | ast::ExprKind::Cast(ref expr, _)
1299         | ast::ExprKind::Field(ref expr, _)
1300         | ast::ExprKind::Try(ref expr)
1301         | ast::ExprKind::Unary(_, ref expr) => is_simple_expr(expr),
1302         ast::ExprKind::Index(ref lhs, ref rhs) => is_simple_expr(lhs) && is_simple_expr(rhs),
1303         ast::ExprKind::Repeat(ref lhs, ref rhs) => {
1304             is_simple_expr(lhs) && is_simple_expr(&*rhs.value)
1305         }
1306         _ => false,
1307     }
1308 }
1309
1310 pub fn is_every_expr_simple(lists: &[OverflowableItem]) -> bool {
1311     lists.iter().all(OverflowableItem::is_simple)
1312 }
1313
1314 pub fn can_be_overflowed_expr(context: &RewriteContext, expr: &ast::Expr, args_len: usize) -> bool {
1315     match expr.node {
1316         ast::ExprKind::Match(..) => {
1317             (context.use_block_indent() && args_len == 1)
1318                 || (context.config.indent_style() == IndentStyle::Visual && args_len > 1)
1319         }
1320         ast::ExprKind::If(..)
1321         | ast::ExprKind::IfLet(..)
1322         | ast::ExprKind::ForLoop(..)
1323         | ast::ExprKind::Loop(..)
1324         | ast::ExprKind::While(..)
1325         | ast::ExprKind::WhileLet(..) => {
1326             context.config.combine_control_expr() && context.use_block_indent() && args_len == 1
1327         }
1328         ast::ExprKind::Block(..) | ast::ExprKind::Closure(..) => {
1329             context.use_block_indent() || context.config.indent_style() == IndentStyle::Visual
1330         }
1331         ast::ExprKind::Array(..)
1332         | ast::ExprKind::Call(..)
1333         | ast::ExprKind::Mac(..)
1334         | ast::ExprKind::MethodCall(..)
1335         | ast::ExprKind::Struct(..)
1336         | ast::ExprKind::Tup(..) => context.use_block_indent() && args_len == 1,
1337         ast::ExprKind::AddrOf(_, ref expr)
1338         | ast::ExprKind::Box(ref expr)
1339         | ast::ExprKind::Try(ref expr)
1340         | ast::ExprKind::Unary(_, ref expr)
1341         | ast::ExprKind::Cast(ref expr, _) => can_be_overflowed_expr(context, expr, args_len),
1342         _ => false,
1343     }
1344 }
1345
1346 pub fn is_nested_call(expr: &ast::Expr) -> bool {
1347     match expr.node {
1348         ast::ExprKind::Call(..) | ast::ExprKind::Mac(..) => true,
1349         ast::ExprKind::AddrOf(_, ref expr)
1350         | ast::ExprKind::Box(ref expr)
1351         | ast::ExprKind::Try(ref expr)
1352         | ast::ExprKind::Unary(_, ref expr)
1353         | ast::ExprKind::Cast(ref expr, _) => is_nested_call(expr),
1354         _ => false,
1355     }
1356 }
1357
1358 /// Return true if a function call or a method call represented by the given span ends with a
1359 /// trailing comma. This function is used when rewriting macro, as adding or removing a trailing
1360 /// comma from macro can potentially break the code.
1361 pub fn span_ends_with_comma(context: &RewriteContext, span: Span) -> bool {
1362     let mut result: bool = Default::default();
1363     let mut prev_char: char = Default::default();
1364     let closing_delimiters = &[')', '}', ']'];
1365
1366     for (kind, c) in CharClasses::new(context.snippet(span).chars()) {
1367         match c {
1368             _ if kind.is_comment() || c.is_whitespace() => continue,
1369             c if closing_delimiters.contains(&c) => {
1370                 result &= !closing_delimiters.contains(&prev_char);
1371             }
1372             ',' => result = true,
1373             _ => result = false,
1374         }
1375         prev_char = c;
1376     }
1377
1378     result
1379 }
1380
1381 fn rewrite_paren(
1382     context: &RewriteContext,
1383     mut subexpr: &ast::Expr,
1384     shape: Shape,
1385     mut span: Span,
1386 ) -> Option<String> {
1387     debug!("rewrite_paren, shape: {:?}", shape);
1388
1389     // Extract comments within parens.
1390     let mut pre_span;
1391     let mut post_span;
1392     let mut pre_comment;
1393     let mut post_comment;
1394     let remove_nested_parens = context.config.remove_nested_parens();
1395     loop {
1396         // 1 = "(" or ")"
1397         pre_span = mk_sp(span.lo() + BytePos(1), subexpr.span.lo());
1398         post_span = mk_sp(subexpr.span.hi(), span.hi() - BytePos(1));
1399         pre_comment = rewrite_missing_comment(pre_span, shape, context)?;
1400         post_comment = rewrite_missing_comment(post_span, shape, context)?;
1401
1402         // Remove nested parens if there are no comments.
1403         if let ast::ExprKind::Paren(ref subsubexpr) = subexpr.node {
1404             if remove_nested_parens && pre_comment.is_empty() && post_comment.is_empty() {
1405                 span = subexpr.span;
1406                 subexpr = subsubexpr;
1407                 continue;
1408             }
1409         }
1410
1411         break;
1412     }
1413
1414     // 1 = `(` and `)`
1415     let sub_shape = shape.offset_left(1)?.sub_width(1)?;
1416     let subexpr_str = subexpr.rewrite(context, sub_shape)?;
1417     let fits_single_line = !pre_comment.contains("//") && !post_comment.contains("//");
1418     if fits_single_line {
1419         Some(format!("({}{}{})", pre_comment, &subexpr_str, post_comment))
1420     } else {
1421         rewrite_paren_in_multi_line(context, subexpr, shape, pre_span, post_span)
1422     }
1423 }
1424
1425 fn rewrite_paren_in_multi_line(
1426     context: &RewriteContext,
1427     subexpr: &ast::Expr,
1428     shape: Shape,
1429     pre_span: Span,
1430     post_span: Span,
1431 ) -> Option<String> {
1432     let nested_indent = shape.indent.block_indent(context.config);
1433     let nested_shape = Shape::indented(nested_indent, context.config);
1434     let pre_comment = rewrite_missing_comment(pre_span, nested_shape, context)?;
1435     let post_comment = rewrite_missing_comment(post_span, nested_shape, context)?;
1436     let subexpr_str = subexpr.rewrite(context, nested_shape)?;
1437
1438     let mut result = String::with_capacity(subexpr_str.len() * 2);
1439     result.push('(');
1440     if !pre_comment.is_empty() {
1441         result.push_str(&nested_indent.to_string_with_newline(context.config));
1442         result.push_str(&pre_comment);
1443     }
1444     result.push_str(&nested_indent.to_string_with_newline(context.config));
1445     result.push_str(&subexpr_str);
1446     if !post_comment.is_empty() {
1447         result.push_str(&nested_indent.to_string_with_newline(context.config));
1448         result.push_str(&post_comment);
1449     }
1450     result.push_str(&shape.indent.to_string_with_newline(context.config));
1451     result.push(')');
1452
1453     Some(result)
1454 }
1455
1456 fn rewrite_index(
1457     expr: &ast::Expr,
1458     index: &ast::Expr,
1459     context: &RewriteContext,
1460     shape: Shape,
1461 ) -> Option<String> {
1462     let expr_str = expr.rewrite(context, shape)?;
1463
1464     let offset = last_line_width(&expr_str) + 1;
1465     let rhs_overhead = shape.rhs_overhead(context.config);
1466     let index_shape = if expr_str.contains('\n') {
1467         Shape::legacy(context.config.max_width(), shape.indent)
1468             .offset_left(offset)
1469             .and_then(|shape| shape.sub_width(1 + rhs_overhead))
1470     } else {
1471         match context.config.indent_style() {
1472             IndentStyle::Block => shape
1473                 .offset_left(offset)
1474                 .and_then(|shape| shape.sub_width(1)),
1475             IndentStyle::Visual => shape.visual_indent(offset).sub_width(offset + 1),
1476         }
1477     };
1478     let orig_index_rw = index_shape.and_then(|s| index.rewrite(context, s));
1479
1480     // Return if index fits in a single line.
1481     match orig_index_rw {
1482         Some(ref index_str) if !index_str.contains('\n') => {
1483             return Some(format!("{}[{}]", expr_str, index_str));
1484         }
1485         _ => (),
1486     }
1487
1488     // Try putting index on the next line and see if it fits in a single line.
1489     let indent = shape.indent.block_indent(context.config);
1490     let index_shape = Shape::indented(indent, context.config).offset_left(1)?;
1491     let index_shape = index_shape.sub_width(1 + rhs_overhead)?;
1492     let new_index_rw = index.rewrite(context, index_shape);
1493     match (orig_index_rw, new_index_rw) {
1494         (_, Some(ref new_index_str)) if !new_index_str.contains('\n') => Some(format!(
1495             "{}{}[{}]",
1496             expr_str,
1497             indent.to_string_with_newline(context.config),
1498             new_index_str,
1499         )),
1500         (None, Some(ref new_index_str)) => Some(format!(
1501             "{}{}[{}]",
1502             expr_str,
1503             indent.to_string_with_newline(context.config),
1504             new_index_str,
1505         )),
1506         (Some(ref index_str), _) => Some(format!("{}[{}]", expr_str, index_str)),
1507         _ => None,
1508     }
1509 }
1510
1511 fn struct_lit_can_be_aligned(fields: &[ast::Field], base: Option<&ast::Expr>) -> bool {
1512     if base.is_some() {
1513         return false;
1514     }
1515
1516     fields.iter().all(|field| !field.is_shorthand)
1517 }
1518
1519 fn rewrite_struct_lit<'a>(
1520     context: &RewriteContext,
1521     path: &ast::Path,
1522     fields: &'a [ast::Field],
1523     base: Option<&'a ast::Expr>,
1524     span: Span,
1525     shape: Shape,
1526 ) -> Option<String> {
1527     debug!("rewrite_struct_lit: shape {:?}", shape);
1528
1529     enum StructLitField<'a> {
1530         Regular(&'a ast::Field),
1531         Base(&'a ast::Expr),
1532     }
1533
1534     // 2 = " {".len()
1535     let path_shape = shape.sub_width(2)?;
1536     let path_str = rewrite_path(context, PathContext::Expr, None, path, path_shape)?;
1537
1538     if fields.is_empty() && base.is_none() {
1539         return Some(format!("{} {{}}", path_str));
1540     }
1541
1542     // Foo { a: Foo } - indent is +3, width is -5.
1543     let (h_shape, v_shape) = struct_lit_shape(shape, context, path_str.len() + 3, 2)?;
1544
1545     let one_line_width = h_shape.map_or(0, |shape| shape.width);
1546     let body_lo = context.snippet_provider.span_after(span, "{");
1547     let fields_str = if struct_lit_can_be_aligned(fields, base)
1548         && context.config.struct_field_align_threshold() > 0
1549     {
1550         rewrite_with_alignment(
1551             fields,
1552             context,
1553             shape,
1554             mk_sp(body_lo, span.hi()),
1555             one_line_width,
1556         )?
1557     } else {
1558         let field_iter = fields
1559             .into_iter()
1560             .map(StructLitField::Regular)
1561             .chain(base.into_iter().map(StructLitField::Base));
1562
1563         let span_lo = |item: &StructLitField| match *item {
1564             StructLitField::Regular(field) => field.span().lo(),
1565             StructLitField::Base(expr) => {
1566                 let last_field_hi = fields.last().map_or(span.lo(), |field| field.span.hi());
1567                 let snippet = context.snippet(mk_sp(last_field_hi, expr.span.lo()));
1568                 let pos = snippet.find_uncommented("..").unwrap();
1569                 last_field_hi + BytePos(pos as u32)
1570             }
1571         };
1572         let span_hi = |item: &StructLitField| match *item {
1573             StructLitField::Regular(field) => field.span().hi(),
1574             StructLitField::Base(expr) => expr.span.hi(),
1575         };
1576         let rewrite = |item: &StructLitField| match *item {
1577             StructLitField::Regular(field) => {
1578                 // The 1 taken from the v_budget is for the comma.
1579                 rewrite_field(context, field, v_shape.sub_width(1)?, 0)
1580             }
1581             StructLitField::Base(expr) => {
1582                 // 2 = ..
1583                 expr.rewrite(context, v_shape.offset_left(2)?)
1584                     .map(|s| format!("..{}", s))
1585             }
1586         };
1587
1588         let items = itemize_list(
1589             context.snippet_provider,
1590             field_iter,
1591             "}",
1592             ",",
1593             span_lo,
1594             span_hi,
1595             rewrite,
1596             body_lo,
1597             span.hi(),
1598             false,
1599         );
1600         let item_vec = items.collect::<Vec<_>>();
1601
1602         let tactic = struct_lit_tactic(h_shape, context, &item_vec);
1603         let nested_shape = shape_for_tactic(tactic, h_shape, v_shape);
1604
1605         let ends_with_comma = span_ends_with_comma(context, span);
1606         let force_no_trailing_comma = context.inside_macro() && !ends_with_comma;
1607
1608         let fmt = struct_lit_formatting(
1609             nested_shape,
1610             tactic,
1611             context,
1612             force_no_trailing_comma || base.is_some() || !context.use_block_indent(),
1613         );
1614
1615         write_list(&item_vec, &fmt)?
1616     };
1617
1618     let fields_str = wrap_struct_field(context, &fields_str, shape, v_shape, one_line_width);
1619     Some(format!("{} {{{}}}", path_str, fields_str))
1620
1621     // FIXME if context.config.indent_style() == Visual, but we run out
1622     // of space, we should fall back to BlockIndent.
1623 }
1624
1625 pub fn wrap_struct_field(
1626     context: &RewriteContext,
1627     fields_str: &str,
1628     shape: Shape,
1629     nested_shape: Shape,
1630     one_line_width: usize,
1631 ) -> String {
1632     if context.config.indent_style() == IndentStyle::Block
1633         && (fields_str.contains('\n')
1634             || !context.config.struct_lit_single_line()
1635             || fields_str.len() > one_line_width)
1636     {
1637         format!(
1638             "{}{}{}",
1639             nested_shape.indent.to_string_with_newline(context.config),
1640             fields_str,
1641             shape.indent.to_string_with_newline(context.config)
1642         )
1643     } else {
1644         // One liner or visual indent.
1645         format!(" {} ", fields_str)
1646     }
1647 }
1648
1649 pub fn struct_lit_field_separator(config: &Config) -> &str {
1650     colon_spaces(config.space_before_colon(), config.space_after_colon())
1651 }
1652
1653 pub fn rewrite_field(
1654     context: &RewriteContext,
1655     field: &ast::Field,
1656     shape: Shape,
1657     prefix_max_width: usize,
1658 ) -> Option<String> {
1659     if contains_skip(&field.attrs) {
1660         return Some(context.snippet(field.span()).to_owned());
1661     }
1662     let mut attrs_str = field.attrs.rewrite(context, shape)?;
1663     if !attrs_str.is_empty() {
1664         attrs_str.push_str(&shape.indent.to_string_with_newline(context.config));
1665     };
1666     let name = context.snippet(field.ident.span);
1667     if field.is_shorthand {
1668         Some(attrs_str + name)
1669     } else {
1670         let mut separator = String::from(struct_lit_field_separator(context.config));
1671         for _ in 0..prefix_max_width.saturating_sub(name.len()) {
1672             separator.push(' ');
1673         }
1674         let overhead = name.len() + separator.len();
1675         let expr_shape = shape.offset_left(overhead)?;
1676         let expr = field.expr.rewrite(context, expr_shape);
1677
1678         match expr {
1679             Some(ref e) if e.as_str() == name && context.config.use_field_init_shorthand() => {
1680                 Some(attrs_str + name)
1681             }
1682             Some(e) => Some(format!("{}{}{}{}", attrs_str, name, separator, e)),
1683             None => {
1684                 let expr_offset = shape.indent.block_indent(context.config);
1685                 let expr = field
1686                     .expr
1687                     .rewrite(context, Shape::indented(expr_offset, context.config));
1688                 expr.map(|s| {
1689                     format!(
1690                         "{}{}:\n{}{}",
1691                         attrs_str,
1692                         name,
1693                         expr_offset.to_string(context.config),
1694                         s
1695                     )
1696                 })
1697             }
1698         }
1699     }
1700 }
1701
1702 fn rewrite_tuple_in_visual_indent_style<'a, T: 'a + IntoOverflowableItem<'a>>(
1703     context: &RewriteContext,
1704     mut items: impl Iterator<Item = &'a T>,
1705     span: Span,
1706     shape: Shape,
1707     is_singleton_tuple: bool,
1708 ) -> Option<String> {
1709     // In case of length 1, need a trailing comma
1710     debug!("rewrite_tuple_in_visual_indent_style {:?}", shape);
1711     if is_singleton_tuple {
1712         // 3 = "(" + ",)"
1713         let nested_shape = shape.sub_width(3)?.visual_indent(1);
1714         return items
1715             .next()
1716             .unwrap()
1717             .rewrite(context, nested_shape)
1718             .map(|s| format!("({},)", s));
1719     }
1720
1721     let list_lo = context.snippet_provider.span_after(span, "(");
1722     let nested_shape = shape.sub_width(2)?.visual_indent(1);
1723     let items = itemize_list(
1724         context.snippet_provider,
1725         items,
1726         ")",
1727         ",",
1728         |item| item.span().lo(),
1729         |item| item.span().hi(),
1730         |item| item.rewrite(context, nested_shape),
1731         list_lo,
1732         span.hi() - BytePos(1),
1733         false,
1734     );
1735     let item_vec: Vec<_> = items.collect();
1736     let tactic = definitive_tactic(
1737         &item_vec,
1738         ListTactic::HorizontalVertical,
1739         Separator::Comma,
1740         nested_shape.width,
1741     );
1742     let fmt = ListFormatting::new(nested_shape, context.config)
1743         .tactic(tactic)
1744         .ends_with_newline(false);
1745     let list_str = write_list(&item_vec, &fmt)?;
1746
1747     Some(format!("({})", list_str))
1748 }
1749
1750 pub fn rewrite_tuple<'a, T: 'a + IntoOverflowableItem<'a>>(
1751     context: &'a RewriteContext,
1752     items: impl Iterator<Item = &'a T>,
1753     span: Span,
1754     shape: Shape,
1755     is_singleton_tuple: bool,
1756 ) -> Option<String> {
1757     debug!("rewrite_tuple {:?}", shape);
1758     if context.use_block_indent() {
1759         // We use the same rule as function calls for rewriting tuples.
1760         let force_tactic = if context.inside_macro() {
1761             if span_ends_with_comma(context, span) {
1762                 Some(SeparatorTactic::Always)
1763             } else {
1764                 Some(SeparatorTactic::Never)
1765             }
1766         } else if is_singleton_tuple {
1767             Some(SeparatorTactic::Always)
1768         } else {
1769             None
1770         };
1771         overflow::rewrite_with_parens(
1772             context,
1773             "",
1774             items,
1775             shape,
1776             span,
1777             context.config.width_heuristics().fn_call_width,
1778             force_tactic,
1779         )
1780     } else {
1781         rewrite_tuple_in_visual_indent_style(context, items, span, shape, is_singleton_tuple)
1782     }
1783 }
1784
1785 pub fn rewrite_unary_prefix<R: Rewrite>(
1786     context: &RewriteContext,
1787     prefix: &str,
1788     rewrite: &R,
1789     shape: Shape,
1790 ) -> Option<String> {
1791     rewrite
1792         .rewrite(context, shape.offset_left(prefix.len())?)
1793         .map(|r| format!("{}{}", prefix, r))
1794 }
1795
1796 // FIXME: this is probably not correct for multi-line Rewrites. we should
1797 // subtract suffix.len() from the last line budget, not the first!
1798 pub fn rewrite_unary_suffix<R: Rewrite>(
1799     context: &RewriteContext,
1800     suffix: &str,
1801     rewrite: &R,
1802     shape: Shape,
1803 ) -> Option<String> {
1804     rewrite
1805         .rewrite(context, shape.sub_width(suffix.len())?)
1806         .map(|mut r| {
1807             r.push_str(suffix);
1808             r
1809         })
1810 }
1811
1812 fn rewrite_unary_op(
1813     context: &RewriteContext,
1814     op: ast::UnOp,
1815     expr: &ast::Expr,
1816     shape: Shape,
1817 ) -> Option<String> {
1818     // For some reason, an UnOp is not spanned like BinOp!
1819     let operator_str = match op {
1820         ast::UnOp::Deref => "*",
1821         ast::UnOp::Not => "!",
1822         ast::UnOp::Neg => "-",
1823     };
1824     rewrite_unary_prefix(context, operator_str, expr, shape)
1825 }
1826
1827 fn rewrite_assignment(
1828     context: &RewriteContext,
1829     lhs: &ast::Expr,
1830     rhs: &ast::Expr,
1831     op: Option<&ast::BinOp>,
1832     shape: Shape,
1833 ) -> Option<String> {
1834     let operator_str = match op {
1835         Some(op) => context.snippet(op.span),
1836         None => "=",
1837     };
1838
1839     // 1 = space between lhs and operator.
1840     let lhs_shape = shape.sub_width(operator_str.len() + 1)?;
1841     let lhs_str = format!("{} {}", lhs.rewrite(context, lhs_shape)?, operator_str);
1842
1843     rewrite_assign_rhs(context, lhs_str, rhs, shape)
1844 }
1845
1846 /// Controls where to put the rhs.
1847 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
1848 pub enum RhsTactics {
1849     /// Use heuristics.
1850     Default,
1851     /// Put the rhs on the next line if it uses multiple line, without extra indentation.
1852     ForceNextLineWithoutIndent,
1853 }
1854
1855 // The left hand side must contain everything up to, and including, the
1856 // assignment operator.
1857 pub fn rewrite_assign_rhs<S: Into<String>, R: Rewrite>(
1858     context: &RewriteContext,
1859     lhs: S,
1860     ex: &R,
1861     shape: Shape,
1862 ) -> Option<String> {
1863     rewrite_assign_rhs_with(context, lhs, ex, shape, RhsTactics::Default)
1864 }
1865
1866 pub fn rewrite_assign_rhs_with<S: Into<String>, R: Rewrite>(
1867     context: &RewriteContext,
1868     lhs: S,
1869     ex: &R,
1870     shape: Shape,
1871     rhs_tactics: RhsTactics,
1872 ) -> Option<String> {
1873     let lhs = lhs.into();
1874     let last_line_width = last_line_width(&lhs).saturating_sub(if lhs.contains('\n') {
1875         shape.indent.width()
1876     } else {
1877         0
1878     });
1879     // 1 = space between operator and rhs.
1880     let orig_shape = shape.offset_left(last_line_width + 1).unwrap_or(Shape {
1881         width: 0,
1882         offset: shape.offset + last_line_width + 1,
1883         ..shape
1884     });
1885     let rhs = choose_rhs(
1886         context,
1887         ex,
1888         orig_shape,
1889         ex.rewrite(context, orig_shape),
1890         rhs_tactics,
1891     )?;
1892     Some(lhs + &rhs)
1893 }
1894
1895 fn choose_rhs<R: Rewrite>(
1896     context: &RewriteContext,
1897     expr: &R,
1898     shape: Shape,
1899     orig_rhs: Option<String>,
1900     rhs_tactics: RhsTactics,
1901 ) -> Option<String> {
1902     match orig_rhs {
1903         Some(ref new_str) if !new_str.contains('\n') && new_str.len() <= shape.width => {
1904             Some(format!(" {}", new_str))
1905         }
1906         _ => {
1907             // Expression did not fit on the same line as the identifier.
1908             // Try splitting the line and see if that works better.
1909             let new_shape = shape_from_rhs_tactic(context, shape, rhs_tactics)?;
1910             let new_rhs = expr.rewrite(context, new_shape);
1911             let new_indent_str = &shape
1912                 .indent
1913                 .block_indent(context.config)
1914                 .to_string_with_newline(context.config);
1915
1916             match (orig_rhs, new_rhs) {
1917                 (Some(ref orig_rhs), Some(ref new_rhs))
1918                     if wrap_str(new_rhs.clone(), context.config.max_width(), new_shape)
1919                         .is_none() =>
1920                 {
1921                     Some(format!(" {}", orig_rhs))
1922                 }
1923                 (Some(ref orig_rhs), Some(ref new_rhs))
1924                     if prefer_next_line(orig_rhs, new_rhs, rhs_tactics) =>
1925                 {
1926                     Some(format!("{}{}", new_indent_str, new_rhs))
1927                 }
1928                 (None, Some(ref new_rhs)) => Some(format!("{}{}", new_indent_str, new_rhs)),
1929                 (None, None) => None,
1930                 (Some(orig_rhs), _) => Some(format!(" {}", orig_rhs)),
1931             }
1932         }
1933     }
1934 }
1935
1936 fn shape_from_rhs_tactic(
1937     context: &RewriteContext,
1938     shape: Shape,
1939     rhs_tactic: RhsTactics,
1940 ) -> Option<Shape> {
1941     match rhs_tactic {
1942         RhsTactics::ForceNextLineWithoutIndent => Some(shape.with_max_width(context.config)),
1943         RhsTactics::Default => {
1944             Shape::indented(shape.indent.block_indent(context.config), context.config)
1945                 .sub_width(shape.rhs_overhead(context.config))
1946         }
1947     }
1948 }
1949
1950 pub fn prefer_next_line(orig_rhs: &str, next_line_rhs: &str, rhs_tactics: RhsTactics) -> bool {
1951     rhs_tactics == RhsTactics::ForceNextLineWithoutIndent
1952         || !next_line_rhs.contains('\n')
1953         || count_newlines(orig_rhs) > count_newlines(next_line_rhs) + 1
1954         || first_line_ends_with(orig_rhs, '(') && !first_line_ends_with(next_line_rhs, '(')
1955         || first_line_ends_with(orig_rhs, '{') && !first_line_ends_with(next_line_rhs, '{')
1956         || first_line_ends_with(orig_rhs, '[') && !first_line_ends_with(next_line_rhs, '[')
1957 }
1958
1959 fn rewrite_expr_addrof(
1960     context: &RewriteContext,
1961     mutability: ast::Mutability,
1962     expr: &ast::Expr,
1963     shape: Shape,
1964 ) -> Option<String> {
1965     let operator_str = match mutability {
1966         ast::Mutability::Immutable => "&",
1967         ast::Mutability::Mutable => "&mut ",
1968     };
1969     rewrite_unary_prefix(context, operator_str, expr, shape)
1970 }
1971
1972 pub fn is_method_call(expr: &ast::Expr) -> bool {
1973     match expr.node {
1974         ast::ExprKind::MethodCall(..) => true,
1975         ast::ExprKind::AddrOf(_, ref expr)
1976         | ast::ExprKind::Box(ref expr)
1977         | ast::ExprKind::Cast(ref expr, _)
1978         | ast::ExprKind::Try(ref expr)
1979         | ast::ExprKind::Unary(_, ref expr) => is_method_call(expr),
1980         _ => false,
1981     }
1982 }